3-Iodothyronamine (T(1)AM) is an endogenous thyroid hormone derivative with distinct biological effects that are largely opposite those of thyroid hormone. Administration of T(1)AM to rodents results in rapid and profound reduction in body temperature, heart rate, and metabolism. The structural similarities between thyroxine, T(1)AM, and monoamine neurotransmitters suggest an intriguing role for T(1)AM as both a neuromodulator and a hormone-like molecule that may constitute a part of thyroid hormone action. Several recent studies into its molecular mechanisms of action have shown that T(1)AM can target extracellular receptors such as the trace amine-associated receptors and the alpha(2A) adrenergic receptor, modulate the membrane transport of neurotransmitters, and serve as a substrate of specific membrane transport cellular uptake machinery. This review discusses recent T(1)AM studies, focusing on both the observed in vivo effects of T(1)AM administration and its actions at the molecular level.